Cardiovascular disease secondary to atherosclerosis is the leading cause of mortality and morbidity worldwide. Growing evidence suggests that the decisive factor determining increased risk for atherosclerotic plaque to cause clinical events is plaque composition rather than the degree of luminal narrowing as measured by angiography.
Atherosclerosis is a form of arteriosclerosis that is characterized by the deposition of plaques containing cholesterol and lipids on the innermost layer of the walls of arteries. Atherosclerosis is currently understood to be a chronic inflammatory disease rather than an inevitable degenerative aging process. The condition usually affects large- and medium-sized arteries. Although such plaque deposits can significantly reduce the blood's flow through an artery, the more serious risk is generally associated with the instigation of an acute clinical event through plaque rupture and thrombosis. In particular, serious damage can occur if an arterial plaque deposit becomes fragile and ruptures, fissures, or ulcerates. Plaque rupture, fissure, or ulcer can cause blood clots to form that block or occlude blood flow and/or break off and travel to other parts of the body. If such blood clots block a blood vessel that feeds the heart, it causes a heart attack. If the blood clot blocks a blood vessel that feeds the brain, it causes a stroke. Similarly, if blood supply to the arms or legs is reduced, it can cause difficulty in walking or light exercise and other collateral damage. Recent studies indicate that thrombotic complications of atherosclerosis remain the leading cause of morbidity and mortality in Western society.
Atherosclerosis may start in childhood and may progress at varying rates as a person ages. In some people, atherosclerosis progresses rapidly, even at a relatively young age. Tobacco smoke greatly worsens atherosclerosis and speeds its growth in the coronary arteries, the aorta, and arteries in the legs. Although some factors that correlate with a higher risk of atherosclerosis are not controllable, such as gender and family history, other correlated risk factors are controllable—including, for example, high blood cholesterol levels, exposure to tobacco smoke, high blood pressure, obesity, and physical inactivity.
The presence and extent of plaque build up in an individual's arteries can be detected using a variety of techniques that are well known in the field including, for example, magnetic resonance imaging (“MRI”), computed tomography (“CT”), X-ray angiography, and ultrasound. Prior art methods for assessing an individual's risk of a clinically significant event such as a stroke or heart attack related to atherosclerotic deposits in an individual's arteries have primarily been directed to evaluating the effect that the plaque deposit has on the blood flow through the artery.
The risk associated with rupture, fissure, or ulceration of plaque, however, may be present even when the plaque deposit does not significantly reduce the flow of blood in an artery. For example, arteries and other blood vessels will sometimes expand or “remodel” in the region of a significant atherosclerotic plaque deposit such that the lumen area does not decrease sufficiently to significantly reduce blood flow. If the plaque ruptures, it may nevertheless create a blood clot that may travel to a critical area to cause a clinical event. The susceptibility of a plaque deposit to structural failure is difficult to determine.
In a clinical context it is often useful to evaluate a particular patient or condition using a simplified scoring system that takes into account a large amount of data and a number of different factors in a simplified manner to rapidly characterize the patient's risk. Such methods can provide a rapid means for evaluating a patient's condition and the urgency of providing appropriate treatments. A well known example of such a scoring system is the Apgar scale ubiquitously used to rapidly judge the health of a new born baby wherein, at one minute and again at five minutes after birth, the infant is evaluated for heart rate, respiration, muscle tone, reflex response, and skin color. Each factor is given a score between zero and two and the scores are added up to provide an immediate assessment of the infant's overall health that is useful in the clinical setting.
With regard to assessing the risk associated with atherosclerosis after imaging a section of a patient's artery having a significant plaque deposit, in the past a medical professional might take hours reviewing the images identifying structures over the region of interest. Such evaluations are clearly not suitable in a clinical setting wherein a rapid evaluation is required.
Therefore, there remains a need for a relatively simple method and system for assessing the risk associated with an atherosclerotic plaque deposit in a patient's artery.